Oleate hydratase from Staphylococcus aureus protects against palmitoleic acid, the major antimicrobial fatty acid produced by mammalian skin.

Oleate hydratases (OhyAs) belong to a large family of bacterial proteins catalyzing the hydration or isomerization of double bonds in unsaturated fatty acids. A Staphylococcus aureus gene ( Sa0102 ) is predicted to encode an OhyA. Here, we recombinantly expressed and purified Sa OhyA and found that it forms a homodimer that requires FAD for activity. Sa OhyA hydrates only unsaturated fatty acids containing cis -9 double bonds, but not fatty acids with trans -9 double bonds or cis double bonds at other positions. Sa OhyA products were not detected in S. aureus phospholipids and were released into the growth medium. S. aureus does not synthesize unsaturated fatty acids, and the Sa OhyA substrates are derived from infection sites. Palmitoleate (16:1(9 Z )) is a major mammalian skin-produced antimicrobial fatty acid that protects against S. aureus infection, and we observed that it is an Sa OhyA substrate and that its hydroxylated derivative is not antimicrobial. Treatment of S. aureus with 24 μm 16:1(9 Z ) immediately arrested growth, followed by growth resumption after a lag period of 2 h. The Δ ohyA mutant strain did not recover from the 16:1(9 Z ) challenge, and increasing Sa OhyA expression using a plasmid system prevented the initial growth arrest. Challenging S. aureus with sapienic acid (16:1(6 Z )), an antimicrobial fatty acid produced only by human skin, arrested growth without recovery in WT, Δ ohyA , and Sa OhyA-overexpressing strains. We conclude that Sa OhyA protects S. aureus from palmitoleic acid, the antimicrobial unsaturated fatty acid produced by most mammals, and that sapienic acid, uniquely produced by humans, counters the OhyA-dependent bacterial defense mechanism.
(© 2019 Subramanian et al.)